Oxidation of silicon is a fundamental technology to CMOS fabrication, dating back to the inception of the integrated circuit. The most common methods for oxidation of silicon rely on thermal processes in ambient of O2, H2O/H2, H2O/O2, O2/H2 or combinations thereof. The hardware used to provide the silicon oxidation process in the IC manufacturing are batch thermal furnaces and RTP. In conventional oxidation systems and processes, high temperature (above 700° C.) is required to provide the activation energy for the oxide growth on silicon or poly-silicon. At temperatures below 700° C., insufficient oxide growth occurs for practical consideration.
Advanced integrated circuit fabrication requires a number of process steps where thin films of silicon oxide are grown on silicon or polysilicon structures. For some applications, the oxidation process must be selective, such that other materials including tungsten are not oxidized. These critical oxidation steps are used for DRAM and FLASH memory and logic devices. Currently thermal processing in either an ambient of O2, H2O/H2, or H2O/O2, at high temperature (>700° C.) is used to perform this oxidation processes. This is typically done with an RTP system such as an ATMOS® system available from Mattson Thermal Products GmbH Dornstadt, Germany. Another single wafer alternative has offered a thermal ‘radical oxidation’ by thermal processing in a low pressure H2/O2 ambient. As device dimensions continue to shrink, a number of serious limitations in the afore-mentioned methods for growing these oxide films have begun to appear. The current processes all require high temperatures in excess of 700° C. and more typically on the order of 900° C. The high temperatures are necessary to obtain the oxide growth rate to make the process practical and in some cases are required for oxide quality. Many of the next generation devices will undergo serious damage at the point in the process flow where the oxide growth is required, if exposed to the combination of high temperature and an oxidizing environment.
At the current state of the art, the various problems facing oxidation include the following examples. For FLASH Poly sidewall oxidation the tunnel oxidation encroachment limits operating temperature to below 700° C. Also, dopant diffusion limits operating temperature to 750° C. For shallow trench isolation (STI) liner oxidation requires conformal oxidation to reduce stress and leakage.
Plasma oxidation as well as UV photon-enhanced oxidation have been described in a number of technical journals and papers. This topic has been an area of research at universities as well. Presently, the leading edge IC manufacturers carry out the most research in this area. Recently, various equipment suppliers have tested hardware in the field that provides various plasma oxidation capabilities.